Method for allocating resources for direct communication between terminals in wireless communication system and device therefor

ABSTRACT

The present application discloses a method for allocating resources for direct communication between terminals in a wireless communication system. Specifically, the method for allocating resources comprises: a step of configuring a first periodic resource so as to transmit multiple messages via direct communication between the terminals; and a step of transmitting the multiple messages by using the first periodic resource if a coding rate corresponding to the first periodic resource is below a maximum coding rate configured by an upper layer, wherein, if the coding rate is equal to or above the maximum coding rate, the first periodic resource is released and a second periodic resource is configured.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of allocating resources for directcommunication between terminals in a wireless communication system andan apparatus therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd generation partnership project long termevolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a diagram schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An evolved universalmobile telecommunications system (E-UMTS) is an advanced version of alegacy universal mobile telecommunications system (UMTS) and basicstandardization thereof is currently underway in 3GPP. E-UMTS may begenerally referred to as an LTE system. For details of the technicalspecifications of UMTS and E-UMTS, reference can be made to Release 7and Release 8 of “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a user equipment (UE), evolvedNode Bs (eNode Bs or eNBs), and an access gateway (AG) which is locatedat an end of an evolved UMTS terrestrial radio access network (E-UTRAN)and connected to an external network. The eNBs may simultaneouslytransmit multiple data streams for a broadcast service, a multicastservice, and/or a unicast service.

One or more cells are present per eNB. A cell is configured to use oneof bandwidths of 1.25, 2.5, 5, 10, 15, and 20 MHz to provide a downlinkor uplink transmission service to multiple UEs. Different cells may beconfigured to provide different bandwidths. The eNB controls datatransmission and reception to and from a plurality of UEs. Regardingdownlink (DL) data, the eNB transmits DL scheduling information tonotify a corresponding UE of a time/frequency domain within which datais to be transmitted, coding, data size, and hybrid automatic repeat andrequest (HARQ)-related information by transmitting DL schedulinginformation to the UE. In addition, regarding uplink (UL) data, the eNBtransmits UL scheduling information to a corresponding UE to inform theUE of an available time/frequency domain, coding, data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic between eNBs may be used. A core network (CN) mayinclude the AG and a network node for user registration of the UE. TheAG manages mobility of a UE on a tracking area (TA) basis, each TAincluding a plurality of cells.

Although radio communication technology has been developed up to LTEbased on wideband code division multiple access (WCDMA), demands andexpectations of users and providers continue to increase. In addition,since other radio access technologies continue to be developed, newadvances in technology are required to secure future competitiveness.For example, decrease of cost per bit, increase of service availability,flexible use of a frequency band, a simplified structure, an openinterface, appropriate power consumption of a UE, etc. are required.

DISCLOSURE OF THE INVENTION Technical Task

Based on the aforementioned discussion, the present invention proposes amethod of allocating resources for direct communication betweenterminals in a wireless communication system and an apparatus thereforin the following.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of allocating a resource for directcommunication between terminals in a wireless communication system,includes the steps of setting a first periodic resource to transmitmultiple messages via the direct communication between the terminals,and if a coding rate corresponding to the first periodic resource isless than a maximum coding rate configured by an upper layer,transmitting the multiple messages using the first periodic resource. Inthis case, if the coding rate is equal to or greater than the maximumcoding rate, the first periodic resource is released and a secondperiodic resource is configured.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, auser equipment performing direct communication between terminals in awireless communication system includes wireless communication moduleconfigured to transceive a signal with a base station or a differentuser equipment, and a processor configured to process the signal, theprocessor configured to set a first periodic resource to transmitmultiple messages via the direct communication between the terminals,the processor, if a coding rate corresponding to the first periodicresource is less than a maximum coding rate configured by an upperlayer, configured to transmit the multiple messages using the firstperiodic resource, the processor, if the coding rate is equal to orgreater than the maximum coding rate, configured to release the firstperiodic resource and set a second periodic resource.

Preferably, if the coding rate is equal to or greater than the maximumcoding rate, the multiple messages are transmitted using the secondperiodic resource.

Preferably, a control signal including information on the first periodicresource and information on the second periodic resource for the directcommunication between the terminals is separately transmitted.Meanwhile, the first periodic resource and the second periodic resourceare randomly selected from at least one resource pool.

Additionally, if the coding rate is equal to or greater than the maximumcoding rate, each of the multiple messages can be divided into submessages of a prescribed size. In this case, the sub messages aretransmitted using the first periodic resource.

Advantageous Effects

According to embodiments of the present invention, it is able toefficiently allocate resources for direct communication betweenterminals and it is able to efficiently transmit and receive a signal.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system;

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a UE and an E-UTRANbased on the 3GPP radio access network specification;

FIG. 3 is a diagram illustrating physical channels used in a 3GPP systemand a general signal transmission method using the same;

FIG. 4 is a diagram illustrating the structure of a radio frame used inan LTE system;

FIG. 5 is a diagram illustrating the structure of a DL radio frame usedin an LTE system;

FIG. 6 is a diagram illustrating the structure of a UL subframe in anLTE system;

FIG. 7 is a conceptual diagram illustrating D2D communication;

FIG. 8 illustrates an example of configuring a resource pool and aresource unit;

FIG. 9 is a diagram illustrating an operation of a UE transmittingfuture resource information in a manner of including the future resourceinformation in a D2D message;

FIG. 10 is a diagram illustrating an operation of a UE transmittingfuture resource information in a manner of including the future resourceinformation in a D2D message;

FIG. 11 is a diagram illustrating an example of periodically andaperiodically allocating resources according to an embodiment of thepresent invention;

FIG. 12 is a block diagram illustrating a communication device accordingto embodiments of the present invention.

BEST MODE Mode for Invention

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments which will be described hereinbelow are examplesin which technical features of the present invention are applied to a3GPP system.

Although the embodiments of the present invention will be describedbased on an LTE system and an LTE-advanced (LTE-A) system, the LTEsystem and the LTE-A system are purely exemplary and the embodiments ofthe present invention can be applied to any communication systemcorresponding to the aforementioned definition. In addition, althoughthe embodiments of the present invention will be described based onfrequency division duplexing (FDD), the FDD mode is purely exemplary andthe embodiments of the present invention can easily be applied tohalf-FDD (H-FDD) or time division duplexing (TDD) with somemodifications.

In the present disclosure, a base station (eNB) may be used as a broadmeaning including a remote radio head (RRH), an eNB, a transmissionpoint (TP), a reception point (RP), a relay, etc.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a UE and an E-UTRANbased on 3GPP radio access network specifications. The control planerefers to a path used for transmission of control messages, which isused by the UE and the network to manage a call. The user plane refersto a path in which data generated in an application layer, e.g. voicedata or Internet packet data, is transmitted.

A physical layer of a first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a media access control (MAC) layer of an upper layer viaa transmission channel. Data is transmitted between the MAC layer andthe physical layer via the transmission channel Data is also transmittedbetween a physical layer of a transmitter and a physical layer of areceiver via a physical channel. The physical channel uses time andfrequency as radio resources. Specifically, the physical channel ismodulated using an orthogonal frequency division multiple Access (OFDMA)scheme in DL and is modulated using a single-carrier frequency divisionmultiple access (SC-FDMA) scheme in UL.

The MAC layer of a second layer provides a service to a radio linkcontrol (RLC) layer of an upper layer via a logical channel. The RLClayer of the second layer supports reliable data transmission. Thefunction of the RLC layer may be implemented by a functional blockwithin the MAC layer. A packet data convergence protocol (PDCP) layer ofthe second layer performs a header compression function to reduceunnecessary control information for efficient transmission of anInternet protocol (IP) packet such as an IPv4 or IPv6 packet in a radiointerface having a relatively narrow bandwidth.

A radio resource control (RRC) layer located at the bottommost portionof a third layer is defined only in the control plane. The RRC layercontrols logical channels, transmission channels, and physical channelsin relation to configuration, re-configuration, and release of radiobearers. A radio bearer refers to a service provided by the second layerto transmit data between the UE and the network. To this end, the RRClayer of the UE and the RRC layer of the network exchange RRC messages.The UE is in an RRC connected mode if an RRC connection has beenestablished between the RRC layer of the radio network and the RRC layerof the UE. Otherwise, the UE is in an RRC idle mode. A non-accessstratum (NAS) layer located at an upper level of the RRC layer performsfunctions such as session management and mobility management.

A single cell consisting of an eNB is set to one of 1.25 MHz, 2.5 MHz, 5MHz, 10 MHz, 15 MHz, and 20 MHz of bandwidths and then provides adownlink or uplink transmission service to a plurality of userequipments. Different cells can be configured to provide correspondingbandwidths, respectively.

DL transmission channels for data transmission from the network to theUE include a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting paging messages,and a DL shared channel (SCH) for transmitting user traffic or controlmessages. Traffic or control messages of a DL multicast or broadcastservice may be transmitted through the DL SCH or may be transmittedthrough an additional DL multicast channel (MCH). Meanwhile, ULtransmission channels for data transmission from the UE to the networkinclude a random access channel (RACH) for transmitting initial controlmessages and a UL SCH for transmitting user traffic or control messages.Logical channels, which are located at an upper level of thetransmission channels and are mapped to the transmission channels,include a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP systemand a general signal transmission method using the same.

When power is turned on or the UE enters a new cell, the UE performs aninitial cell search procedure such as acquisition of synchronizationwith an eNB (S301). To this end, the UE may adjust synchronization withthe eNB by receiving a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) from the eNB and acquireinformation such as a cell identity (ID). Thereafter, the UE may acquirebroadcast information within the cell by receiving a physical broadcastchannel from the eNB. In the initial cell search procedure, the UE maymonitor a DL channel state by receiving a downlink reference signal(DLRS).

Upon completion of the initial cell search procedure, the UE may acquiremore detailed system information by receiving a physical downlinkcontrol channel (PDCCH) and receiving a physical downlink shared channel(PDSCH) based on information carried on the PDCCH (S302).

Meanwhile, if the UE initially accesses the eNB or if radio resourcesfor signal transmission to the eNB are not present, the UE may perform arandom access procedure (S303 to S306) with the eNB. To this end, the UEmay transmit a specific sequence through a physical random accesschannel (PRACH) as a preamble (S303 and S305) and receive a responsemessage to the preamble through the PDCCH and the PDSCH associated withthe PDCCH (S304 and S306). In the case of a contention-based randomaccess procedure, the UE may additionally perform a contentionresolution procedure.

After performing the above procedures, the UE may receive a PDCCH/PDSCH(S307) and transmit a physical uplink shared channel (PUSCH)/physicaluplink control channel (PUCCH) (S308), as a general UL/DL signaltransmission procedure. Especially, the UE receives downlink controlinformation (DCI) through the PDCCH. The DCI includes controlinformation such as resource allocation information for the UE and hasdifferent formats according to use purpose thereof.

Meanwhile, control information that the UE transmits to the eNB on UL orreceives from the eNB on DL includes a DL/UL acknowledgment/negativeacknowledgment (ACK/NACK) signal, a channel quality indicator (CQI), aprecoding matrix index (PMI), a rank indicator (RI), and the like. Inthe 3GPP LTE system, the UE may transmit the control information such asCQI/PMI/RI through a PUSCH and/or a PUCCH.

FIG. 4 is a diagram illustrating the structure of a radio frame used inan LTE system.

Referring to FIG. 4, the radio frame has a length of 10 ms(327200×T_(s)) and includes 10 equal-sized subframes. Each of thesubframes has a length of 1 ms and includes two slots. Each slot has alength of 0.5 ms (15360 T_(s)). In this case, T_(s) denotes a samplingtime represented by T_(s)=11(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns).Each slot includes a plurality of OFDM symbols in the time domain andincludes a plurality of resource blocks (RBs) in the frequency domain.In the LTE system, one RB includes 12 subcarriers×7 (or 6) OFDM symbols.A transmission time interval (TTI), which is a unit time for datatransmission, may be determined in units of one or more subframes. Theabove-described structure of the radio frame is purely exemplary andvarious modifications may be made in the number of subframes included ina radio frame, the number of slots included in a subframe, or the numberof OFDM symbols included in a slot.

FIG. 5 is a diagram illustrating control channels contained in a controlregion of one subframe in a DL radio frame.

Referring to FIG. 5, one subframe includes 14 OFDM symbols. The first tothird ones of the 14 OFDM symbols may be used as a control region andthe remaining 11 to 13 OFDM symbols may be used as a data region,according to subframe configuration. In FIG. 5, R1 to R4 representreference signals (RSs) or pilot signals for antennas 0 to 3,respectively. The RSs are fixed to a predetermined pattern within thesubframe irrespective of the control region and the data region. Controlchannels are allocated to resources unused for RSs in the controlregion. Traffic channels are allocated to resources unused for RSs inthe data region. The control channels allocated to the control regioninclude a physical control format indicator channel (PCFICH), a physicalhybrid-ARQ indicator channel (PHICH), a physical downlink controlchannel (PDCCH), etc.

The PCFICH, physical control format indicator channel, informs a UE ofthe number of OFDM symbols used for the PDCCH in every subframe. ThePCFICH is located in the first OFDM symbol and is configured withpriority over the PHICH and the PDCCH. The PCFICH is composed of 4resource element groups (REGs) and each of the REGs is distributed overthe control region based on a cell ID. One REG includes 4 resourceelements (REs). An RE indicates a minimum physical resource defined asone subcarrier by one OFDM symbol. The PCFICH value indicates values of1 to 3 or values of 2 to 4 depending on bandwidth and is modulated usingquadrature phase shift keying (QPSK).

The PHICH, physical hybrid-ARQ indicator channel, is used to carry aHARQ ACK/NACK signal for UL transmission. That is, the PHICH indicates achannel through which DL ACK/NACK information for UL HARQ istransmitted. The PHICH includes one REG and is cell-specificallyscrambled. The ACK/NACK signal is indicated by 1 bit and is modulatedusing binary phase shift keying (BPSK). The modulated ACK/NACK signal isspread with a spreading factor (SF) of 2 or 4. A plurality of PHICHsmapped to the same resource constitutes a PHICH group. The number ofPHICHs multiplexed to the PHICH group is determined depending on thenumber of spreading codes. The PHICH (group) is repeated three times toobtain diversity gain in the frequency domain and/or the time domain.

The PDCCH is allocated to the first n OFDM symbols of a subframe. Inthis case, n is an integer equal to or greater than 1, indicated by thePCFICH. The PDCCH is composed of one or more control channel elements(CCEs). The PDCCH informs each UE or UE group of information associatedwith resource allocation of transmission channels, that is, a pagingchannel (PCH) and a downlink shared channel (DL-SCH), UL schedulinggrant, HARQ information, etc. The PCH and the DL-SCH are transmittedthrough a PDSCH. Therefore, the eNB and the UE transmit and receive datathrough the PDSCH except for particular control information or servicedata.

Information indicating to which UE or UEs PDSCH data is to betransmitted and information indicating how UEs should receive and decodethe PDSCH data are transmitted on the PDCCH. For example, assuming thata cyclic redundancy check (CRC) of a specific PDCCH is masked by a radionetwork temporary identity (RNTI) ‘A’ and information about datatransmitted using a radio resource ‘B’ (e.g. frequency location) andusing DCI format ‘C’, i.e. transport format information (e.g. atransport block size, a modulation scheme, coding information, etc.), istransmitted in a specific subframe, a UE located in a cell monitors thePDCCH, i.e. blind-decodes the PDCCH, using RNTI information thereof in asearch space. If one or more UEs having RNTI ‘A’ are present, the UEsreceive the PDCCH and receive a PDSCH indicated by ‘B’ and ‘C’ based onthe received information of the PDCCH.

FIG. 6 is a diagram illustrating the structure of a UL subframe in anLTE system.

Referring to FIG. 6, an uplink subframe is divided into a region towhich a PUCCH is allocated to transmit control information and a regionto which a PUSCH is allocated to transmit user data. The PUSCH isallocated to the middle of the subframe, whereas the PUCCH is allocatedto both ends of a data region in the frequency domain. The controlinformation transmitted on the PUCCH includes an ACK/NACK, a channelquality indicator (CQI) representing a downlink channel state, an R1 forMultiple Input and Multiple Output (MIMO), a scheduling request (SR)indicating a request for allocation of UL resources, etc. A PUCCH of aUE uses one RB occupying different frequencies in each slot of asubframe. That is, two RBs allocated to the PUCCH frequency-hop over theslot boundary. Particularly, PUCCHs for m=0, m=1, m=2, and m=3 areallocated to a subframe in FIG. 6.

FIG. 7 is a conceptual diagram illustrating direct D2D communication.

Referring to FIG. 7, during D2D communication (i.e., direct D2Dcommunication) in which the UE wirelessly communicates with another UE,the eNB may transmit a scheduling message for indicating D2Dtransmission/reception. The UE participating in D2D communication mayreceive a D2D scheduling message from the eNB, and performs Tx/Rxoperations indicated by the D2D scheduling message. Here, although a UEmeans a user terminal, a network entity such as an eNB may be regardedas a UE when transmitting and receiving a signal according to acommunication method between UEs. Hereinafter, a link between UEs isreferred to as a D2D link and a link for communication between a UE andan eNB is referred to as an NU link. Or, a link directly connectedbetween UEs can be referred to as a sidelink as a concept in contrast toan uplink and a downlink.

Meanwhile, a case that a UE1 selects a resource unit corresponding to aspecific resource from a resource pool corresponding to a set ofresources and transmits a D2D signal using the selected resource unit isexplained in the following. In this case, if the UE1 is located withincoverage of an eNB, the eNB can inform the UE1 of the resource pool. Ifthe UE1 is located at the outside of the coverage of the eNB, adifferent UE may inform the UE1 of the resource pool or the resourcepool can be determined by predetermined resources. In general, theresource pool includes a plurality of resource units. Each UE selectsone or more resource units and may be then able to use the selectedresource unit(s) to transmit a D2D signal of the UE.

FIG. 8 is a diagram for configuration examples of a resource pool and aresource unit.

Referring to FIG. 8, it exemplary shows a case of defining N_(F)*N_(T)number of resource units in total by dividing total frequency resourcesinto N_(F) and dividing total time resources into N_(T). In particular,it shows that a corresponding resource pool is repeated with an intervalof N_(T) subframes. Particularly, one resource unit may periodically andrepeatedly appear. Or, an index of a physical resource unit to which onelogical resource unit is mapped may change in a predetermined pattern toobtain a diversity effect in time domain or frequency domain. In thisresource unit structure, the resource pool may correspond to a set ofresource units capable of being used for a UE to transmit a D2D signal.

The resource pool can be classified into various types. First of all,the resource pool can be classified according to contents of a D2Dsignal transmitted from the resource pool. For example, as shown in 1)to 3) in the following, the contents of the D2D signal can be classifiedinto SA, a D2D data channel, and a discovery signal and a separateresource pool can be configured according to each of the contents.

1) Scheduling assignment (SA): SA may correspond to a signal includinginformation on a resource position of a D2D data channel, information onMCS (modulation and coding scheme) necessary for demodulating a datachannel, information on a MIMO transmission scheme, and the like. The SAinformation can be transmitted on an identical resource unit in a mannerof being multiplexed with D2D data. In this case, an SA resource poolmay correspond to a pool of resources in which SA and D2D data aretransmitted in a manner of being multiplexed.

2) D2D data channel: A D2D data channel corresponds to a channel used bya transmission UE to transmit user data. If SA and a D2D data aretransmitted on an identical resource unit in a manner of beingmultiplexed, a resource element (RE), which is used to transmit SAinformation in a specific resource unit of an SA resource pool, can alsobe used for transmitting D2D data in a D2D data channel resource pool.

3) Discovery signal: A discovery signal corresponds to a resource poolfor transmitting a signal that enables a neighboring UE to discover atransmission UE transmitting information such as ID of the UE, and thelike.

4) Synchronization signal/channel: A synchronization signal/channel canalso be referred to as a sidelink synchronization signal or a sidelinkbroadcast channel. The synchronization signal/channel corresponds to aresource pool used for a transmission UE to transmit a synchronizationsignal/channel and information related to synchronization to a receptionUE. By doing so, the reception UE is able to match time/frequencysynchronization with the transmission UE.

SA and data are able to use resource pools separated from each other ina subframe. Yet, if a UE is able to transmit the SA and the data at thesame time in a single subframe, two types of resource pools can beconfigured in the same subframe.

When a UE transmits a D2D message or an uplink message at specifictiming, the UE can include information on a time position and/or afrequency position of a resource to be used in the future, i.e.,information on a future resource, in the D2D message or the uplinkmessage.

FIG. 9 is a diagram illustrating an operation of a UE transmittingfuture resource information in a manner of including the future resourceinformation in a D2D message.

Referring to FIG. 9, when a UE transmits a D2D message which isgenerated with a certain period P, the UE may start to transmit amessage 1 generated at timing t from the timing t+x. In this case, themessage 1 can include a fact that a message 2, which is to be generatedat a next period, is going to be transmitted at timing t+P+y using aspecific frequency resource. By doing so, the UE can inform a differentUE of information on a future resource. In this case, time x or time ycorresponds to delay time between message generation and actualtransmission. In general, a message generation period P may have a valueequal to or greater than 100 ms. The information on the future resourcecan be transmitted via such a separate control channel as SA. Or, theinformation can be transmitted in a manner of being included in a datachannel (e.g., a partial field of MAC header).

Or, a future resource can be designated using a method of designating aresource position in a plurality of periods via a single transmission ofa control channel FIG. 10 is a diagram illustrating an operation of a UEtransmitting future resource information in a manner of including thefuture resource information in a D2D message. The UE can transmit aperiodically generated message to an eNB or a neighboring UE via adesignated resource of the abovementioned form.

The operation is defined as periodic resource allocation. The periodicresource allocation means that a resource to be used by a UEperiodically appears and a resource position of a next period isdetermined in advance in a previous period. A periodic resource can bedesignated by an eNB or a UE can autonomously determine the periodicresource.

Although a specific UE performs periodic resource allocation, thespecific UE may use an undesignated resource. In particular, if aresource to be used for transmitting a message at a specific period isnot designated in a previous period, although the specific UE performsthe periodic resource allocation, the UE should use an undesignatedresource. This is referred to as aperiodic resource allocation.

For example, when a different message is suddenly generated immediatelyafter a message is transmitted at a prescribed period, if it isnecessary to transmit the different message prior to a (time) resourceof a next period, it may additionally use aperiodic resource allocation.When a UE autonomously determines a resource, the UE may use anaperiodic resource according to a prescribed rule. When an eNBdesignates a resource, a UE may ask the eNB to allocate an aperiodicresource and the eNB can allocate an appropriate resource to the UE.

In the following, an operation effective for a case that periodicresource allocation and aperiodic resource allocation coexist isexplained.

If a specific message is generated, it is necessary for a UE todetermine a resource allocation scheme to be used for the specificmessage among periodic resource allocation and aperiodic resourceallocation.

As a method of determining a resource allocation method, it may considera bearer and a logical channel ID at which a message is generated and apriority of a message. An eNB can configure the periodic resourceallocation to be used for a message generated at a specific bearer and alogical channel ID or a message having a specific priority. If a messageis generated at a different specific bearer and logical channel ID or amessage has a different specific priority, the eNB can configure theaperiodic resource allocation to be used for the message. When a UEgenerates a message, the UE generates the message at an appropriatebearer and a logical channel ID according to an attribute of the messageand a resource allocation method necessary for the message and may beable to assign an appropriate priority to the message.

As a different method of determining a resource allocation method, itmay consider a message size. In the following, a size of a message isdefined by the number of bits constructing a specific message generatedin an upper layer. Yet, the same principle can be interpreted andapplied to a size of a buffer in which a message is stored. Inparticular, if a message size is big, it may indicate that the greatamounts of data are stored in a buffer at specific timing.

In general, a resource of a fixed size is designated via the periodicresource allocation. In this case, although a message is mapped to aperiodic resource, a size of the message may vary. In particular, if amessage of a big size is suddenly generated, it may be difficult to mapthe message to a stationary periodic resource. In this case, a UE cantransmit the message temporarily using the aperiodic resourceallocation. For example, it may be able to set an upper limit and alower limit of a message size. If a size of a message is within thelimit, the message is transmitted using a resource designated as aperiodic resource as it is. If a size of a message is out of the limit,the message is transmitted using an aperiodic resource. An eNB canconfigure the upper limit and the lower limit of the message size inadvance via higher layer signaling such as RRC or the like. The upperlimit and the lower limit can be implemented in a form of an upper limitand a lower limit of a coding rate. In particular, the upper limit ofthe message size and the upper limit of the coding rate can beconfigured by a value capable of achieving minimum stability necessaryfor transmitting a corresponding message. In particular, if a message ofa size greater than the upper limit is transmitted, it may indicate thatit is unable to achieve minimally required stability.

If a UE transmits a specific message using an aperiodic resource, aperiodic resource of a specific period is not used. Yet, if a differentUE reads a periodic resource allocation message of the UE and emptiesout a corresponding resource, resource waste occurs. Hence, it ispreferable for the UE to perform aperiodic resource allocation whileutilizing a periodic resource reserved by the UE. For example, in thiscase, if the different UE does not use an aperiodic resource, the UE canconfigure the aperiodic resource to mandatorily include the periodicresource reserved by the UE.

It may be able to configure a size of an aperiodic resource to be equalto or less than a prescribed level compared to a size of a periodicresource. In this case, in case of using a different resource (includinga part of a legacy periodic resource) via aperiodic resource allocationwithout using a previously used periodic resource, it may be able tocontinuously use the aperiodic resource. Consequently, when an aperiodicresource is used without using a periodic resource, it can be consideredas a position and/or a size of a periodic resource is changed or aperiodic resource is reselected.

When periodic resource allocation or aperiodic resource allocation isselected according to the message size, it can be interpreted as todetermine whether or not a position and/or a size of a periodic resourceis changed according to the message size.

Meanwhile, if a size of a message is instantaneously changed, themessage is transmitted by selecting an aperiodic resource one time and anext message is configured to use an original periodic resource. On thecontrary, if a size of a message is continuously changed, it is moreprofitable to continuously use a resource once selected as an aperiodicresource. More generally, if a message size or a buffer size exceeds aprescribed limit and is not appropriate for a legacy periodic resource,for example, if a situation incapable of performing transmissioncontinuously occurs N times, it may be able to configure a periodicresource to be selected again. Specifically, an N^(th) selectedaperiodic resource can be continuously used in a manner of beingregarded as a new periodic resource.

When the aforementioned operation is performed, it may be able totransmit a message of a size exceeding a prescribed limit using both aperiodic resource and an aperiodic resource. In particular, when amessage of a big size is generated, the message is preferentiallytransmitted using a periodically allocated resource. If it is determinedthat a reception success rate of the message is lower than a targetlevel, the same message is transmitted one more time using aperiodicresource allocation. By doing so, it may be able to expect that areception UE successfully receives the message via one of the twotransmissions. Or, it may be able to configure the reception UE toattempt to receive the message by combining the two transmissions. Inparticular, when the reception UE receives the message by combining thetwo transmissions, it is necessary for the reception UE to identify atransmission signal capable of being combined. Hence, a HARQ process IDshould be included in scheduling control information. Or, an indicatorindicating whether or not it is feasible to combine a transmissionsignal according to periodic resource allocation transmitted in the sameperiod can be included in an aperiodic resource allocation signal.

As a variation of the operation of transmitting the message (or, data ofa size exceeding a prescribed limit stored in a buffer) of the sizeexceeding the prescribed limit using both the periodic resource and theaperiodic resource, the message of the size exceeding the prescribedlimit can be divided into a plurality of transport blocks. Inparticular, a part of a plurality of the transport blocks is transmittedvia a periodic resource and the remaining part of a plurality of thetransport blocks can be transmitted via an aperiodic resource. Inparticular, if a message size (or, a buffer size) does not exceed aprescribed limit, it is regulated that a future resource designated in atransmission of a previous period is used only. And, a transmissionperformed using an aperiodic resource, which uses an additionalresource, is not allowed.

This operation has a characteristic in that a resource allocation schemein use is selected from among periodic allocation and aperiodicallocation according to a size of a message (or, a buffer) for a datagenerated by a single QoS (quality of service) or a data generated by aservice having a priority. In particular, as mentioned in the foregoingdescription, in a situation that a data having a specific priority(e.g., an emergency data to be promptly transmitted) does not occur, ifa UE designates a future resource via a previous transmission, the UEcan perform transmission using a resource rather than a resourcedesignated as the future resource only when a size of a message (or, abuffer) is equal to or greater than a prescribed level.

As a different meaning, when periodic resource allocation is determinedfor a specific communication service (e.g., a communication servicebroadcasting a location, speed, a device status, etc. of a vehicle witha prescribed period), a prescribed resource is periodically used, andthe determined periodic resource allocation and the prescribed resourceare notified to a receiving end, a transmitting end may allow aperiodicresource allocation to be used for the service only when a size of amessage (or, a buffer) generated by the service at specific timingexceeds a prescribed limit.

FIG. 11 is a diagram illustrating an example of periodically andaperiodically allocating resources according to an embodiment of thepresent invention. In particular, in FIG. 11, assume a case that a sizeof a message corresponding to the same service varies when a periodicresource is allocated with a period of P.

Referring to FIG. 11, it is able to see that a message of size A and amessage of size A+a are generated at the timing t and the timing t+P,respectively. In this case, since a size of a is equal to or less than aprescribed level, a periodic resource is used only.

On the contrary, when a message of size A+b is generated at the timingt+2P, since a size of b is equal to greater than a prescribed level, aUE divides the message into two parts. A part of a size of A istransmitted via a periodic resource and then a part of a size B isadditionally transmitted via aperiodic resource allocation.

Meanwhile, a UE reads a resource allocation message of a different UEand may be then able to avoid a resource collision. In this case, if theabovementioned operation of the present invention is applied, a casethat the same UE examines a case of allocating resources of two types atthe same time may occur. One is to examine the case via periodicresource allocation and another is to examine the case via aperiodicresource allocation. Since a single UE is unable to use two resources atthe same time, the UE may regard a periodically allocated resource as atemporarily available resource by recognizing that a corresponding UE isgoing to use an aperiodically allocated resource only. This informationmay correspond to information utilized by a different UE to performaperiodic resource allocation.

To this end, an ID of a transmission UE can be included in a resourceallocation control message. Yet, if a size of the control message islimitative, it is difficult to include the ID of the transmission UE inthe control message. In this case, a plurality of UEs may transmit thesame ID information to the control message. Hence, it may consider thatall resources designated by a periodic resource allocation controlmessage or an aperiodic resource allocation control message are actuallyused by a different UE.

When a resource is periodically configured, if a resource isaperiodically allocated, a message to be transmitted is additionallygenerated. In this case, a UE selects an aperiodic resource using aresource unoccupied by a different UE and may be then able to transmitthe message. In this case, the UE regards a resource designated by theUE to perform periodic resource allocation as a resource occupied by thedifferent UE to select an aperiodic resource. For example, if the UErandomly selects a part of resources unoccupied by the different UE froma resource pool, similar to a resource occupied by the different UE, aresource designated by the UE using periodic resource allocation isexcluded from a target of aperiodic resource selection. In this case, ifa specific aperiodic resource is (partly) overlapped with a periodicallocation resource, the aperiodic resource can be excluded from theselection.

Moreover, if it is difficult for the UE to transmit two messages (or,two physical channels) at the same time, the UE can exclude both theresource designated by the UE using periodic resource allocation and aUE belonging to the same timing from a target of aperiodic resourceselection. The UE is unable to perform aperiodic transmission at thecorresponding timing because the UE performs periodic transmission atthe timing. Hence, it is necessary to prevent a resource of a differentfrequency from being selected as an aperiodic transmission resource atthe timing.

Or, in order to prevent a single UE from excessively occupying aperiodic resource and an aperiodic resource, a resource periodicallyconfigured by the UE is also included in a target of aperiodic resourceselection. When a resource is selected according to a series ofselection procedures, it may perform transmission according to aperiodicresource selection using the resource. In this case, a transmissionaccording to periodic resource allocation can be dropped. In this case,although the periodic resource allocation is overlapped with theaperiodic resource allocation in partial time only, since it isdifficult for a different UE to know the fact, the entire periodicresource allocation of a corresponding period can be dropped. Or, it maybe able to move a position of a periodic resource to a differentposition or reduce a size of a resource occupied by a periodic messagetemporarily.

Meanwhile, in a situation that a periodic resource is fixedly reserved,a UE may designate a size of a transport block all the time to moreefficiently process a variable message.

In a general resource allocation structure, a size of a transmittedtransport block is automatically determined according to a modulationorder in use and a size of a resource in use. And, in a legacy LTEsystem, scheduling information included in a control channel informs areception UE of a modulation order and a resource size and the receptionUE identifies a size of a transport block using the schedulinginformation. This property is also maintained in periodic resourceallocation including SPS (semi-persistent scheduling). However,according to the aforementioned situation, while a message size varies,a modulation order and a resource size are fixed by previous controlinformation. Hence, a size of a transport block is fixed. Consequently,zero padding is performed on a message, thereby increasing inefficiency.

In order to solve the inefficiency, it may consider a) or b) describedin the following.

a) In case of performing periodic resource allocation, a position of aresource is designated only and a modulation order is separatelydesignated whenever a message is transmitted. In particular, while aposition of a resource used in a specific period is determined in aprevious period or previous timing, a modulation order is differentlydesignated according to a period. Since information on a modulationorder is transmitted together with data, the information can betransmitted via a part of a periodically allocated resource. Or, theinformation can be transmitted to a reception UE by differentiating asequence or a position of a reference signal according to a modulationorder.

As an example of transmitting the information on the modulation ordervia a part of a periodic allocation resource, separate channel coding isapplied to the information on the modulation order irrespective of dataand the information is multiplexed with a data signal. In this case,since it is necessary for a reception UE to identify a resource fromwhich the information on the modulation order is transmitted, it ispreferable to fix a position of the resource. A signal transmitted by aUE may have a form of SC-FDMA to reduce PARR. In this case, themodulation order information is transmitted from all or a part ofSC-FDMA symbols. The modulation order information and data are mapped toa different logical RE of a symbol and DFT spreading is performed on theinformation and the data to generate a time domain transmission signal.

As an example of using a sequence of a reference signal, CS (cyclicshift) or an OCC (orthogonal cover code) to be applied to a referencesignal sequence are mapped to a specific modulation order in advance anda UE can transmit a reference signal using CS or OCC corresponding to amodulation order of each transmission timing. If a size of a message isgetting bigger, a size of a transport block is increased using highorder modulation to map the message to a fixed resource size. If a sizeof a message is getting smaller, it may be able to more stably transmitthe message using low order modulation.

b) A modulation order as well as a resource position can be determinedin a previous period. And, a size of a transport block is designatedusing separate control information. Similar to the a), the informationcan be transmitted via a part of a periodically allocated resource. Or,the information can be forwarded to a reception UE by differentiating asequence or a position of a reference signal according to a size of atransport block.

As an example of transmitting information on a transport block size viaa part of a periodic allocation resource, separate channel coding isapplied to the information irrespective of data and the information ismultiplexed with a data signal. In this case, since it is necessary fora reception UE to identify a resource from which the information on thetransport block size is transmitted, it is preferable to fix a positionof the resource. A signal transmitted by a UE may have a form of SC-FDMAto reduce PARR. In this case, the information on the transport blocksize is transmitted from all or a part of SC-FDMA symbols. Themodulation and data signaling are mapped to a different logical RE of asymbol and DFT spreading is performed on the information and the data togenerate a time domain transmission signal.

As an example of using a sequence of a reference signal, CS or an OCC tobe applied to a reference signal sequence are mapped to a specifictransport block size in advance and a UE can transmit a reference signalusing CS or OCC corresponding to a transport block size of eachtransmission timing. A size of a transport block available for a givenresource size and a modulation order is restricted to several sizes. Asize most suitable for an actual message (e.g., a smallest size or asize closest to the smallest size among sizes equal to or greater thanthe message) is selected and the selected size is used as a transportblock size of a corresponding period. In particular, if a size of amessage is small, it may be able to reduce a transport block size. Itmay be able to more obtain a channel coding gain in preparation for acase of performing zero padding in a transport block generation stage.

While resource information is transmitted in a previous period orprevious timing, it may be able to make a modulation order and atransport block size vary at the timing at which data is transmitted bycombining the a) scheme and the b) scheme.

Meanwhile, if a message or a transport block of a different size istransmitted in a resource of a fixed size according to theaforementioned operation, since a coding rate is changed, it isdifficult to have uniform performance. In particular, if a size of amessage or a transport block is big, since it is necessary to transmitmore bits with a given resource, a transmission success rate isdeteriorated.

In order to offset the deterioration of the transmission success rate,it may be able to control transmit power according to a size of amessage or a transport block transmitted in a periodically allocatedresource and a modulation order in use. In particular, in case oftransmitting more bits, stronger power is used. As a different meaning,in case of transmitting a message or a transport block of a small size,a UE reduces transmit power to enable closely located UEs to use acorresponding resource together with the UE. By doing so, it may be ableto enhance overall system performance.

In this case, if transmit power is too low, it is difficult to detect asignal itself and difficult to guarantee minimum performance indetecting a different control signal transmitted together with thesignal. In order to prevent the abovementioned problem, it may be ableto provide minimum transmit power to a UE to be used by the UE forperforming transmission. In this case, if there is a signal transmittedon a different carrier, it may be able to transmit a bigger message withstronger power by additionally receiving power. In particular, it meansthat a ratio of distributing power with a signal transmitted on adifferent carrier is changed according to a size of a message to betransmitted in a periodically allocated resource.

For example, when a different signal is transmitted on a second carrierwhile the aforementioned operation is performed via a first carrier,i.e., in case of transmitting PUSCH triggered via a UL grant receivedfrom an eNB, minimum power used for performing transmission on the firstcarrier is designated and power rather than the minimum power can beused for performing transmission on the second carrier. In this case,the minimum power guaranteed on the first carrier may vary depending ona message size on the first carrier. In case of transmitting a smallermessage, smaller minimum power can be guaranteed. As a result, when a UEtransmits a bigger message on the first carrier, it is necessary toguarantee more power. As a result, power usable for performingtransmission on the second carrier is reduced. More specifically, theminimum power guaranteed on the first carrier is determined according toa size of a message transmitted on the first carrier or a coding rate.When a basic minimum power is configured, it may be able to add power asmuch as a prescribed offset for a bigger message size or a bigger codingrate.

As a different example, it may be able to define minimum powerguaranteed on the second carrier. A value of the minimum power may varydepending on a size of a message transmitted on the first carrier. Inparticular, in case of transmitting a bigger message on the firstcarrier, the minimum power guaranteed on the second carrier can bereduced. Specifically, the minimum power guaranteed on the secondcarrier is determined according to a size of a message transmitted onthe first carrier or a coding rate. When a basic minimum power of thesecond carrier is configured, it may be able to reduce power as much asa prescribed offset for a bigger message size transmitted on the firstcarrier or a bigger coding rate.

Meanwhile, when an eNB allocates a periodic resource to a UE, if anamount of data occurred on the UE is too excessive to be transmitted tothe periodic resource, it is preferable to inform the eNB of the amountof data and receive more resources from the eNB. In this case, theresources allocated by the eNB may correspond to a resource forperforming UL transmission to the eNB or a resource for performing D2Dtransmission to a different UE. In most cases, a message occurred on theUE can be transmitted using the periodic resource allocated by the eNB.Yet, as mentioned in the foregoing description, if data exceeding aprescribed limit occurs, it is necessary to have an additional resource.

Specifically, the UE may inform the eNB that an additional resource isrequired. To this end, the UE may use an SR (scheduling request) and/ora BSR (buffer status report). In this case, it is necessary to minimizesignaling overhead. If the previously allocated periodic resource issufficient enough for minimizing the signaling overhead, the UE can omittransmission of the SR and/or the BSR. In other word, the SR and/or theBSR are transmitted only when a data size of a service to be transmittedby the periodic resource exceeds a prescribed limit to induce the eNB toallocate a resource. In particular, if the size of the data occurred onthe UE exists at a region capable of stably transmitting the data usingthe previously allocated periodic resource, the UE continuously uses theperiodic resource without transmitting the unnecessary SR/BSR. By doingso, it may be able to reduce signaling overhead and power consumption ofthe UE.

As a different method, when a resource periodically allocated by the eNBcorresponds to a resource for performing D2D transmission, if dataoccurred on the UE has a size exceeding a prescribed limit, the UEautonomously selects a resource in addition to the periodicallyallocated resource and the autonomously selected resource can be usedfor transmitting the data together with the periodically allocatedresource. The abovementioned operation basically follows the principlementioned earlier in FIG. 11. Yet, the periodic resource is allocated bythe eNB, whereas the additionally used resource is autonomously selectedby the UE without resource allocation of the eNB.

When the UE autonomously selects a resource, the UE identifies resourceallocation information of a different UE to avoid a collision with aresource selected by the different UE. Or, the UE measures energy ofeach resource to preferentially select a resource rather than a resourcealready used by the different UE.

FIG. 12 is a block diagram of a communication apparatus according to anembodiment of the present invention.

Referring to FIG. 12, a communication device 1200 includes a processor1210, a memory 1220, a radio frequency (RF) module 1230, a displaymodule 1240, and a user interface (UI) module 1250.

The communication device 1200 is illustrated for convenience ofdescription and some modules may be omitted. The communication device1200 may further include necessary modules. Some modules of thecommunication device 1200 may be further divided into sub-modules. Theprocessor 1200 is configured to perform operations according to theembodiments of the present invention exemplarily described withreference to the drawings. Specifically, for a detailed description ofoperations of the processor 1200, reference may be made to thedescription described with reference to FIGS. 1 to 11.

The memory 1220 is connected to the processor 1210 and stores operatingsystems, applications, program code, data, and the like. The RF module1230 is connected to the processor 1210 and performs a function ofconverting a baseband signal into a radio signal or converting a radiosignal into a baseband signal. For this, the RF module 1230 performsanalog conversion, amplification, filtering, and frequency upconversionor performs inverse processes thereof. The display module 1240 isconnected to the processor 1210 and displays various types ofinformation. The display module 1240 may include, but is not limited to,a well-known element such as a liquid crystal display (LCD), a lightemitting diode (LED), or an organic light emitting diode (OLED). The UImodule 1250 is connected to the processor 1210 and may include acombination of well-known UIs such as a keypad and a touchscreen.

The above-described embodiments are combinations of elements andfeatures of the present invention in a predetermined manner. Each of theelements or features may be considered selective unless mentionedotherwise. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. In the appendedclaims, claims that are not explicitly dependent upon each other may ofcourse be combined to provide an embodiment or new claims can be addedthrough amendment after the application is filed.

In this document, a specific operation described as performed by an eNBmay be performed by an upper node of the eNB. Namely, it is apparentthat, in a network comprised of a plurality of network nodes includingan eNB, various operations performed for communication with a UE may beperformed by the eNB, or network nodes other than the eNB. The term eNBmay be replaced with the terms fixed station, Node B, eNode B (eNB),access point, etc.

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, orcombinations thereof. In the case of a hardware configuration, theembodiments of the present invention may be implemented by one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In the case of a firmware or software configuration, the methodaccording to the embodiments of the present invention may be implementedby a module, a procedure, or a function, which performs functions oroperations described above. For example, software code may be stored ina memory unit and then may be executed by a processor. The memory unitmay be located inside or outside the processor to transmit and receivedata to and from the processor through various well-known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

Although a method of allocating a resource for performing directcommunication between terminals in a wireless communication system andan apparatus therefor are described with reference to examples appliedto 3GPP LTE system, it may be applicable to various kinds of wirelesscommunication systems as well as the 3GPP LTE system.

1. A method of transmitting multiple messages via a sidelink by a userequipment (UE) in a wireless communication system, the methodcomprising: configuring a sidelink resource; receiving the multiplemessages from an upper layer; if the sidelink resource accommodates themultiple messages by using a maximum coding rate configured by the upperlayer, transmitting the multiple messages using the configured sidelinkresource to a counterpart UE; and if the sidelink resource cannotaccommodate at least one of the multiple messages by using the maximumcoding rate, re-configuring the sidelink resource.
 2. The method ofclaim 1, if the sidelink resource cannot accommodate the at least one ofthe multiple messages by using the maximum coding rate, furthercomprising transmitting the multiple messages using the re-configuredsidelink resource.
 3. (canceled)
 4. The method of claim 1, wherein theconfigured sidelink resource and the re-configured sidelink resource arerandomly selected from at least one resource pool.
 5. The method ofclaim 1, wherein if the sidelink resource cannot accommodate the atleast one of the multiple messages by using the maximum coding rate,each of the multiple messages is divided into sub-messages of apredefined size, and wherein the sub-messages are transmitted using theconfigured sidelink resource.
 6. A user equipment (UE) performingsidelink communication in a wireless communication system, comprising: aradio frequency (RF) unit; and a processor connected with the RF unit,wherein the processor configures a sidelink resource, receives multiplemessages from an upper layer, wherein, if the sidelink resourceaccommodates the multiple messages by using a maximum coding rateconfigured by the upper layer, the processor transmits the multiplemessages using the configured sidelink resource to a counterpart UE,wherein, if the sidelink resource cannot accommodate at least one of themultiple messages by using the maximum coding rate, the processorre-configures the sidelink resource.
 7. The user equipment of claim 6,wherein, if the sidelink resource cannot accommodate the at least one ofthe multiple messages by using the maximum coding rate, the processortransmits the multiple messages using the re-configured sidelinkresource.
 8. (canceled)
 9. The user equipment of claim 6, wherein theconfigured sidelink resource and the re-configured sidelink resource arerandomly selected from at least one resource pool.
 10. The userequipment of claim 6, wherein if the sidelink resource cannotaccommodate the at least one of the multiple messages by using themaximum coding rate, each of the multiple messages is divided intosub-messages of a predefined size, and wherein the processor transmitsthe multiple messages using the re-configured sidelink resource.